Method for forming fin field effect transistor (FINFET) device structure

ABSTRACT

A FinFET device structure and method for forming the same are provided. The method includes forming a plurality of fin structures over a substrate, and the substrate includes a first region and a second region. The method includes forming a plurality of isolation structures surrounding the fin structures, and a top surface of each of the isolation structures is lower than a top surface of each of the fin structures, and the isolation structures include first isolation structures over the first region and second isolation structures over the second region. The method includes forming a mask layer on the first isolation structures to expose the second isolation structures and removing a portion of the second isolation structures, such that a top surface of each of the second isolation structures is lower than a top surface of each of the first isolation structures.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon. Many integrated circuits are typically manufactured on a single semiconductor wafer, and individual dies on the wafer are singulated by sawing between the integrated circuits along a scribe line. The individual dies are typically packaged separately, in multi-chip modules, for example, or in other types of packaging.

As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, challenges from both fabrication and design issues have resulted in the development of three-dimensional designs, such as the fin field effect transistor (FinFET). FinFETs are fabricated with a thin vertical “fin” (or fin structure) extending from a substrate. The channel of the FinFET is formed in this vertical fin. A gate is provided over the fin. The advantages of a FinFET may include reducing the short channel effect and providing a higher current flow.

Although existing FinFET devices and methods of fabricating FinFET devices have generally been adequate for their intended purposes, they have not been entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It should be noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1I show perspective representations of various stages of forming a FinFET device structure, in accordance with some embodiments of the disclosure.

FIGS. 2A-2I show cross-sectional representations of various stages of forming the FinFET device structure shown in FIGS. 1A-1I.

FIGS. 3A-3H show perspective representations of various stages of forming a FinFET device structure, in accordance with some embodiments of the disclosure.

FIGS. 4A-4H show cross-sectional representations of various stages of forming the FinFET device structure shown in FIGS. 3A-3H.

FIGS. 5A-5E show perspective representations of various stages of forming a FinFET device structure, in accordance with some embodiments of the disclosure.

FIGS. 6A-6E show cross-sectional representations of various stages of forming the FinFET device structure shown in FIGS. 5A-5E.

FIGS. 7A-7D show perspective representations of various stages of forming a FinFET device structure, in accordance with some embodiments of the disclosure.

FIGS. 8A-8D show cross-sectional representations of various stages of forming the FinFET device structure shown in FIGS. 7A-7D.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the subject matter provided. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Some variations of the embodiments are described. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements. It should be understood that additional operations can be provided before, during, and after the method, and some of the operations described can be replaced or eliminated for other embodiments of the method.

The fins may be patterned by any suitable method. For example, the fins may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Generally, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in one embodiment, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-alignment process. The sacrificial layer is then removed, and the remaining spacers may then be used to pattern the fins.

Embodiments for forming a fin field effect transistor (FinFET) device structure are provided. FIGS. 1A-1I show perspective representations of various stages of forming a FinFET device structure 100, in accordance with some embodiments of the disclosure. FIGS. 2A-2I show cross-sectional representations of various stages of forming the FinFET device structure 100 shown in FIGS. 1A-1I. FIGS. 2A-2I show cross-sectional representations taken along line aa′ in FIGS. 1A-1I.

Referring to FIG. 1A, a substrate 102 is provided. The substrate 102 includes a first region 11 and a second region 12. The substrate 102 may be made of silicon or other semiconductor materials. In some embodiments, the substrate 102 is a silicon wafer. Alternatively or additionally, the substrate 102 may include other elementary semiconductor materials such as germanium. In some embodiments, the substrate 102 is made of a compound semiconductor such as silicon carbide, gallium arsenic, indium arsenide, or indium phosphide. In some embodiments, the substrate 102 is made of an alloy semiconductor such as silicon germanium, silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. In some embodiments, the substrate 102 includes an epitaxial layer. For example, the substrate 102 has an epitaxial layer overlying a bulk semiconductor.

Afterwards, a dielectric layer 104 and a mask layer 106 are formed over the substrate 102, and a photoresist layer 108 is formed over the mask layer 106. The photoresist layer 108 is patterned by a patterning process. The patterning process includes a photolithography process and an etching process. The photolithography process includes photoresist coating (e.g., spin-on coating), soft baking, mask aligning, exposure, post-exposure baking, developing the photoresist, rinsing and drying (e.g., hard baking). The etching process may include a dry etching process or a wet etching process.

The dielectric layer 104 is a buffer layer between the substrate 102 and the mask layer 106. In addition, the dielectric layer 104 is used as a stop layer when the mask layer 106 is removed. The dielectric layer 104 may be made of silicon oxide. The mask layer 106 may be made of silicon oxide, silicon nitride, silicon oxynitride, or another applicable material. In some other embodiments, more than one mask layer 106 is formed over the dielectric layer 104.

The dielectric layer 104 and the mask layer 106 are formed by deposition processes, such as a chemical vapor deposition (CVD) process, a high-density plasma chemical vapor deposition (HDPCVD) process, a spin-on process, a sputtering process, or another applicable process.

As shown in FIGS. 1B and 2B, after the photoresist layer 108 is patterned, the dielectric layer 104 and the mask layer 106 are patterned by using the patterned photoresist layer 108 as a mask, in accordance with some embodiments. As a result, a patterned dielectric layer 104 and a patterned mask layer 106 are obtained. Afterwards, the patterned photoresist layer 108 is removed.

Afterwards, an etching process is performed on the substrate 102 to form a number of fin structures 110 a, 110 b by using the patterned dielectric layer 104 and the patterned mask layer 106 as a mask. The fin structures 110 a, 110 b include first fin structures 110 a in the first region 11 and second fin structures 110 b in the second region 12. In some embodiments, each of the fin structures 110 a, 110 b has a width that gradually increases from the top portion to the bottom portion. In other words, each of the fin structures 110 a, 110 b has a tapered fin width which is gradually tapered from the bottom portion to the top portion.

The etching process may be a dry etching process or a wet etching process. In some embodiments, the substrate 102 is etched using a dry etching process. The dry etching process includes using a fluorine-based etchant gas, such as SF₆, C_(x)F_(y), NF₃ or a combination thereof. The etching process may be a time-controlled process, and continue until the fin structures 110 a, 110 b reach a predetermined height.

Before forming the isolation layer 112 (shown in FIG. 3C), a thermal oxidation process may be optionally performed on the fin structures 110 a, 110 b to repair any damage to the sidewall surfaces of the fin structures 110 a, 110 b during the etching process. It should be noted that although only four fin structures 110 a, 110 b shown in FIGS. 1A-1I and FIGS. 2A-2I, the number of the fin structures 110 a, 110 b may be changed according to actual application.

As shown in FIGS. 1C and 2C, after the fin structures 110 a, 110 b are formed, the isolation layer 112 is formed to cover the fin structures 110 a, 110 b over the substrate 102, in accordance with some embodiments.

In some embodiments, the isolation layer 112 is made of silicon oxide, silicon nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), or another low-k dielectric material. The isolation layer 112 may be deposited by a deposition process, such as a chemical vapor deposition (CVD) process, a spin-on-glass process, or another applicable process.

Afterwards, as shown in FIGS. 1D and 2D, the isolation layer 112 is thinned or planarized to expose the top surface of the patterned mask layer 106. In some embodiments, the insulating layer 112 is thinned by a chemical mechanical polishing (CMP) process.

Afterwards, as shown in FIGS. 1E and 2E, a portion of the insulating layer 112 is removed to form a number of isolation structures 114 a, 114 b, in accordance with some embodiments. In addition, the patterned dielectric layer 104 and the patterned mask layer 106 are removed. The isolation structures 114 a, 114 b include first isolation structures 114 a over the first region 11 and second isolation structures 114 b over the second region 12. The isolation structures 114 a, 114 b may be a shallow trench isolation (STI) structure surrounding the fin structures 110 a, 110 b.

A lower portion of each of the fin structures 110 a, 110 b is surrounded by each of the isolation structures 114 a, 114 b, and an upper portion of each of the fin structures 110 a, 110 b protrudes from each of the isolation structures 114 a, 114 b. In other words, a portion of each of the fin structures 110 a, 110 b is embedded in each of the isolation structures 114 a, 114 b. The isolation structures 114 a, 114 b prevent electrical interference or crosstalk.

Afterwards, as shown in FIGS. 1F and 2F, a mask layer 210 is formed over the first fin structures 110 a and the first isolation structures 114 a, and a portion of the second isolation structures 114 b is removed, in accordance with some embodiments. In some embodiments, an etching process 212 is performed on the second isolation structures 114 b to remove the portion of the second isolation structures 114 b.

The mask layer 210 covers the first isolation structures 114 a, but the second isolation structures 114 b are exposed. In some embodiments, the mask layer 210 is made of photoresist materials, such as polybenzoxazole (PBO), SU-8-photo-sensitive epoxy, film type polymer materials and/or the like.

Next, as shown in FIGS. 1G and 2G, after the etching process 212, the mask layer 210 is removed, in accordance with some embodiments. As a result, a top surface of each of the first isolation structures 114 a is higher than a top surface of each of the second isolation structures 114 b. In other words, the top surface of each of the second isolation structures 114 b is lower than the top surface of each of the first isolation structures 114 a.

Each of the first fin structures 110 a has a first fin height H₁ measured from a top surface of each of the first fin structures 110 a to a top surface of each of the first isolation structures 114 a. Each of the second fin structures 110 b has a second fin height H₂ measured from a top surface of each of the second fin structures 110 b to a top surface of each of the second isolation structures 110 b. The first fin height H₁ is smaller than the second fin height H₂. In some embodiments, the first fin height H₁ is in a range from about 40 nm to about 60 nm. In some embodiments, the second fin height H₂ is in a range from about 40.1 nm to about 80 nm. The higher difference ΔH between the first fin height H₁ and the second fin height H₂ is in a range from about 0.1 nm to about 20 nm.

Each of the first isolation structures 114 a has a first depth D₁, and each of the second isolation structures 114 b has a second depth D₂. In some embodiments, the first depth D₁ of each of the first isolation structures 114 a is greater than the second depth D₂ of each of the second isolation structures 114 b.

In the first region 11, a first pitch P₁ is between two adjacent first fin structures 110 a, and a second pitch P₂ is between two adjacent second fin structures 110 b. In some embodiments, the first pitch P₁ is in a range from about 20 nm to about 60 nm. In some embodiments, the second pitch P₂ is in n a range from about 20 nm to about 60 nm.

As shown in FIG. 2G, a first angle θ1 between the sidewall surface of each of the fin structures 110 a, 110 b and the top surface of each of the isolation structures 114 a, 114 b. In some embodiments, the first angle θ1 is in a range from about 95 degrees to about 120 degrees. Each of the first structures 110 a has a top width W₁ and a bottom width W₂, and the top width W₁ is smaller than the bottom width W₂.

Afterwards, as shown in FIGS. 1H and 2H, a gate dielectric layer 116 is formed on the fin structures 110 a, 110 b, the isolation structures 114 a, 114 b, and a gate electrode layer 118 is formed on the gate dielectric layer 116, in accordance with some embodiments. A gate structure 120 is constructed by the gate dielectric layer 116 and the gate electrode layer 118. In some embodiments, the gate dielectric layer 116 is a dummy gate dielectric layer and the gate electrode layer 118 is a dummy gate electrode layer. The dummy gate dielectric layer and the dummy gate electrode layer may be replaced by the following steps to form a real gate structure with a high-k dielectric layer and a metal gate electrode layer.

In some embodiments, the gate dielectric layer 116 may include dielectric materials, such as silicon oxide, silicon nitride, silicon oxynitride, dielectric material(s) with high dielectric constant (high-k), or combinations thereof. In some embodiments, the gate electrode layer 118 is made of polysilicon. The gate dielectric layer 116 and the gate electrode layer 118 are independently formed by a deposition process, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), high density plasma CVD (HDPCVD), metal organic CVD (MOCVD), or plasma enhanced CVD (PECVD).

Afterwards, a pair of spacer layers 122 are formed on opposite sidewalls of the gate structure 120, in accordance with some embodiments. More specifically, the spacer layers 122 are formed on sidewall surfaces of the gate electrode layer 118. The spacer layers 122 may be made of silicon oxide, silicon nitride, silicon oxynitride, and/or dielectric materials. In some embodiments, the spacer layers 122 are formed by a chemical vapor deposition (CVD) process, a spin-on-glass process, or another applicable process.

Afterwards, a top portion of the fin structures 110 a, 110 b is removed to form a recess (not shown), and the source/drain (S/D) structures (not shown) are formed in the recess. The source/drain (S/D) structures are formed on opposite of the gate structure 120. In some embodiments, the S/D structures are strained source/drain structures. In some embodiments, the S/D structures are formed by growing a strained material in the recesses of the fin structures 110 a, 110 b by an epitaxial (epi) process. In addition, the lattice constant of the strained material may be different from the lattice constant of the substrate 102.

In some embodiments, the source/drain structures include Ge, SiGe, InAs, InGaAs, InSb, GaAs, GaSb, InAlP, InP, or a combination thereof. The epitaxial process may include a selective epitaxy growth (SEG) process, CVD deposition techniques (e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, or other suitable epi processes.

In some embodiments, after the S/D structures are formed, a contact etch stop layer (CESL) (not shown) is formed on the S/D structures and the gate structure 120. In some embodiments, the contact etch stop layer is made of silicon nitride, silicon oxynitride, and/or other applicable materials. The contact etch stop layer may be formed by plasma enhanced CVD, low pressure CVD, ALD, or other applicable processes.

Afterwards, as shown in FIGS. 1I and 2I, an inter-layer dielectric (ILD) material is formed over the fin structures 110 a, 110 b over the substrate 102, in accordance with some embodiments. Next, the ILD material is planarized to form the ILD structure 126.

The ILD structure 126 has a first portion in the first region 11 and a second portion in the second region 12. A bottom surface of the first portion of the ILD structure 126 is higher than a bottom surface of the second portion of the ILD structure 126. The ILD structure 126 may include multilayers made of multiple dielectric materials, such as silicon oxide, silicon nitride, silicon oxynitride, tetraethoxysilane (TEOS), phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), low-k dielectric material, and/or other applicable dielectric materials. Examples of low-k dielectric materials include, but are not limited to, fluorinated silica glass (FSG), carbon doped silicon oxide, amorphous fluorinated carbon, parylene, bis-benzocyclobutenes (BCB), or polyimide. The ILD structure 126 may be formed by chemical vapor deposition (CVD), physical vapor deposition, (PVD), atomic layer deposition (ALD), spin-on coating, or other applicable processes.

Afterwards, the dummy gate dielectric layer 116 and the dummy gate electrode layer 118 are removed to form a trench, and the real gate dielectric layer and metal gate electrode layer (not shown) are filled into the trench. In some embodiments, a work function layer (not shown) may be formed between the gate dielectric layer and the gate electrode layer. The work function layer (not shown) is made of metal material, and the metal material may include N-work-function metal or P-work-function metal. The N-work-function metal includes tungsten (W), copper (Cu), titanium (Ti), silver (Ag), aluminum (Al), titanium aluminum alloy (TiAl), titanium aluminum nitride (TiAlN), tantalum carbide (TaC), tantalum carbon nitride (TaCN), tantalum silicon nitride (TaSiN), manganese (Mn), zirconium (Zr) or a combination thereof. The P-work-function metal includes titanium nitride (TiN), tungsten nitride (WN), tantalum nitride (TaN), ruthenium (Ru) or a combination thereof. Afterwards, the FinFET device structure 200 continues to form other devices or structures.

In the first embodiment, the FinFET device structure 100 with different fin heights is obtained by performing two etching processes. The first etching process is performed to simultaneously remove a portion of the first isolation structures 114 a and a portion of the second isolation structures 114 b. The second etching process with an extra mask layer is used to further remove the second isolation structures 114 b to a predetermined depth. Compared with forming the second isolation structure by using one etching process, the etching amount is controlled more precisely by the two etching process. Especially when the FinFET device structure has a fine spacing (or smaller pitch), which is in the range of nanometers (nm), between neighboring gate structures, removal of the bottom portion of the second isolation structures 114 b becomes difficult due to the shadow effect. In order to control the fin height more precisely, the second isolation structures 114 b are etched by a first rough etching process and a second accurate etching process. In addition, the second etching process is compatible with the FinFET processes.

Furthermore, the FinFET device structure 100 with different fin heights can improve the cutoff frequency (Ft), and therefore the FinFET device structure 100 can be used in the high-frequency device.

FIGS. 3A-3H show perspective representations of various stages of forming a FinFET device structure 200, in accordance with some embodiments of the disclosure. FIGS. 4A-4H show cross-sectional representations of various stages of forming the FinFET device structure 200 shown in FIGS. 3A-3H. FIGS. 4A-4H show cross-sectional representations taken along line aa′ in FIGS. 3A-3H. Some processes and materials used to form the FinFET device structure 200 are similar to, or the same as, those used to form the FinFET structure 100 and are not repeated herein.

The structures in FIGS. 3A-3B are similar to the structures in FIGS. 1A-1B and the structures in FIGS. 4A-4B are similar to the structures in FIGS. 2A-2B, and are not repeated herein.

Afterwards, as shown in FIGS. 3C and 4C, a mask layer 220 is formed over the second fin structures 110 b in the second region 12, and a portion of the first fin structures 110 is removed, in accordance with some embodiments. An etching process 222 is performed on the first fin structures 110 over the first region 11 to remove or shape a portion of the first fin structures 110 a. In some embodiments, the etching process 222 is a dry etching process with etching gas, such as Cl₂, HB, CF₄ or another applicable gas. Each of the first fin structures 110 a has a constant width from a bottom portion to a top portion.

Next, as shown in FIGS. 3D and 4D, after the etching process 222, the mask layer 220 is removed, in accordance with some embodiments. The mask layer 220 may be removed by a dry etching process or a wet etching process.

The first fin structures 110 a in the first region 11 and the second fin structures 110 b in the second region 12 have different fin profiles. The first fin structures 110 a are etching twice and have straighter sidewall surface when compared with the second fin structures 110 b.

Afterwards, as shown in FIGS. 3E and 4E, the isolation layer 112 is formed to cover the fin structures 110 a, 110 b over the substrate 102, in accordance with some embodiments.

Afterwards, as shown in FIGS. 3F and 4F, the isolation layer 112 is thinned or planarized, and then is etched to form the first isolation structures 114 a and the second isolation structures 114 b, in accordance with some embodiments. As a result, the first fin structures 110 a are surrounded by the first isolation structures 114 a, and the second fin structures 110 b are surrounded by the second isolation structures 114 b.

Each of the first fin structures 110 a has a first fin height H₁, and each of the second fin structures 110 b has a second fin height H₂. In some embodiments, the first fin height H₁ is equal to the second fin height H₂. Each of the second structures 110 b has a top width W₁ and a bottom width W₂, and the top width W₁ is smaller than the bottom width W₂. Each of the first fin structures 110 a has a constant width from a bottom portion to a top portion.

A third angle Θ₃ is between the sidewall surface of each of the first fin structures 110 a and the top surface of the first isolation structures 114 a. The sidewall surface of each of the first fin structures 110 is substantially orthogonal to the top surface of each of the first isolation structures 114 a. A fourth angle Θ₄ is between the sidewall surface of each of the second fin structures 110 b and the top surface of the second isolation structures 114 b. In some embodiments, the third angle Θ₃ is smaller than the fourth angle Θ₄. In some embodiments, the third angle Θ₃ is in a range from about 80 degrees to about 90 degrees. In some embodiments, the fourth angle Θ₄ is in a range from about 80 degrees to about 120 degrees. The angle difference between the third angle Θ₃ and the fourth angle Θ₄ is in a range from about 0 degree to about 30 degrees.

Next, as shown in FIGS. 3G and 4G, the gate structure 120 is formed on the fin structures 110 a, 110 b, the isolation structures 114 a, 114 b, in accordance with some embodiments. The gate structure 120 includes the gate dielectric layer 116 and the gate electrode layer 118. Afterwards, a pair of spacer layers 122 are formed on opposite sidewalls of the gate structure 120.

Afterwards, as shown in FIGS. 3H and 4H, the ILD structure 126 is formed on the fin structures 110 a, 110 b and the isolation structures 114 a, 114 b, in accordance with some embodiments. Afterwards, the FinFET device structure 200 continues to form other devices or structures.

In the second embodiment, the FinFET device structure 200 is formed to have different fin profiles. The first fin structures 110 a in the first region 11 have straighter sidewall surfaces, and the second fin structures 110 b in the second region 12 have sloped sidewall surfaces. By forming different fin profiles, the parasite capacitance (C) of the FinFET device structures 200 is reduced, and therefore the cutoff frequency (Ft) of FinFET device structure 200 is improved. Therefore, the FinFET device structure 200 can be used in the high-frequency device.

FIGS. 5A-5E show perspective representations of various stages of forming a FinFET device structure 300, in accordance with some embodiments of the disclosure. FIGS. 6A-6E show cross-sectional representations of various stages of forming the FinFET device structure 300 shown in FIGS. 5A-5E. FIGS. 6A-6E show cross-sectional representations taken along line aa′ in FIGS. 5A-5E. Some processes and materials used to form the FinFET device structure 300 are similar to, or the same as, those used to form the FinFET structure 100 and are not repeated herein.

As shown in FIGS. 5A and 6A, after the fin structures 110 a, 110 b are formed, the isolation layer 112 is formed to cover the fin structures 110 a, 110 b over the substrate 102, in accordance with some embodiments.

Afterwards, as shown in FIGS. 5B and 6B, the isolation layer 112 is thinned or planarized to expose the top surface of the patterned mask layer 106. In some embodiments, the insulating layer 112 is thinned by a chemical mechanical polishing (CMP) process.

Afterwards, as shown in FIGS. 5C and 6C, a portion of the insulating layer 112 is removed to form a number of isolation structures 114, in accordance with some embodiments. In addition, the patterned dielectric layer 104 and the patterned mask layer 106 are removed. The isolation structures 114 include first isolation structures 114 a over the first region 11 and second isolation structures 114 b over the second region 12.

It should be noted that the second pitch P₂ between two adjacent second fin structures 110 b is greater than the first pitch P₁ between two adjacent first fin structures 110 a due to the second fin structures 110 b with a narrower top portion. More of the second isolation structures 114 b are removed compared with the first isolation structures 114 a since the etching gas may easily pass through the wider opening (or wider pitch P₂). The first isolation structures 114 a are removed less, such that the top surface of each of the first isolation structures 114 a is higher than the top surface of each of the second isolation structures 114 b.

The first fin height H₁ of each of the first fin structures 110 a is smaller than the second fin height H₂ of each of the second fin structures 110 b. The first depth D₁ of each of the first isolation structures 114 a is greater than the second depth D₂ of each of the second isolation structures 114 b. In addition, the third angle Θ₃ is smaller than the fourth angle Θ₄.

Afterwards, as shown in FIGS. 5D and 6D, the gate structure 120 is formed on the fin structures 110 a, 110 b, the isolation structures 114 a, 114 b, in accordance with some embodiments. The gate structure 120 includes the gate dielectric layer 116 and the gate electrode layer 118. Afterwards, a pair of spacer layers 122 are formed on opposite sidewalls of the gate structure 120.

Next, as shown in FIGS. 5E and 6E, the ILD structure 126 is formed on the fin structures 110 a, 110 b and the isolation structures 114 a, 114 b, in accordance with some embodiments. The ILD structure 126 has a first portion in the first region 11 and a second portion in the second region 12. A bottom surface of the first portion of the ILD structure 126 is higher than a bottom surface of the second portion of the ILD structure 126. Afterwards, the FinFET device structure 300 continues to form other devices or structures.

In the third embodiment, the FinFET device structure 300 is formed to have different fin profiles and different fin heights. The first fin structures 110 a in the first region 11 have straighter sidewall surfaces and lower first fin height H₁, and the second fin structures 110 b in the second region 12 have sloped sidewall surfaces and higher second fin height H₂. By forming different fin profiles and fin heights, the cutoff frequency (Ft) of FinFET device structure 300 is improved. Therefore, the FinFET device structure 300 can be used in the high-frequency device.

FIGS. 7A-7D show perspective representations of various stages of forming a FinFET device structure 400, in accordance with some embodiments of the disclosure. FIGS. 8A-8D show cross-sectional representations of various stages of forming the FinFET device structure 400 shown in FIGS. 7A-7D. FIGS. 8A-8D show cross-sectional representations taken along line aa′ in FIGS. 7A-7D. Some processes and materials used to form the FinFET device structure 400 are similar to, or the same as, those used to form the FinFET structure 100 and are not repeated herein.

As shown in FIGS. 7A and 8A, each of the first fin structures 110 a in the first region 11 has constant fin width, and each of the second fin structures 110 b in the second region 12 has a tapered width which is gradually tapered from the bottom portion to the top portion. The isolation layer 112 over the fin structures 110 a, 110 b and then is thinned or planarized to expose the top surface of the patterned mask layer 106. In some embodiments, the insulating layer 112 is thinned by a chemical mechanical polishing (CMP) process.

Next, as shown in FIGS. 7B and 8B, a portion of the insulating layer 112 is removed to form a number of isolation structures 114, in accordance with some embodiments. In addition, the patterned dielectric layer 104 and the patterned mask layer 106 are removed. The first isolation structures 114 a over the first region 11 and the second isolation structures 114 b over the second region 12 both have the same height.

Afterwards, as shown in FIGS. 7C and 8C, a mask layer 230 is formed over the first fin structures 110 a and the first isolation structures 114 a, and a portion of the second isolation structures 114 b is removed, in accordance with some embodiments. In some embodiments, an etching process 232 is performed on the second isolation structures 114 b to remove the portion of the second isolation structures 114 b.

Next, as shown in FIGS. 7D and 8D, after the etching process 232, the mask layer 230 is removed, in accordance with some embodiments. The mask layer 230 may be removed by a dry etching process or a wet etching process.

The first fin structures 110 a in the first region 11 and the second fin structures 110 b in the second region 12 have different fin profiles and different fin heights. The second fin structures 110 b in the second region 12 are etched twice and have sloped sidewall surfaces. Afterwards, the FinFET device structure 400 continues to form other devices and structures.

In the fourth embodiment, the FinFET device structure 400 is formed to have different fin profiles and different fin heights. The first fin structures 110 a in the first region 11 have straighter sidewall surfaces and lower first fin height H₁, and the second fin structures 110 b in the second region 12 have sloped sidewall surfaces and higher second fin height H₂. By forming different fin profiles and fin heights, the cutoff frequency (Ft) of FinFET device structure 400 is improved. Therefore, the FinFET device structure 400 can be used in the high-frequency device.

In the first embodiment, the first fin structures 110 a and the second fin structures 110 b have different fin heights. In the second embodiment, the first fin structures 110 a and the second fin structures 110 b have different fin profiles. In the third and fourth embodiments, the first fin structures 110 a and the second fin structures 110 b have different fin heights and have different fin profiles. By forming the different fin height and/or different fin profiles, the parasite capacitance (C) of the FinFET device structures 100, 200, 300, 400 may be reduced and therefore the cutoff frequency (Ft) of the FinFET device structures 100, 200, 300, 400 is improved.

Embodiments for forming a FinFET device structure and method for formation of the same are provided. The FinFET device structure includes an isolation structure formed over a substrate, and a fin structure extends from the isolation structure. The FinFET device structure with different fin heights is achieved by using two etching processes. A portion of the isolation structures is etched twice to control the etching amount more precisely. The FinFET device structure with different fin heights and/or different fin profiles to reduce the parasite capacitance (C) of the FinFET device structures. Therefore, the performance of the FinFET device structures is improved.

In some embodiments, a method for forming a FinFET device structure is provided. The method includes forming a plurality of fin structures over a substrate, and the substrate includes a first region and a second region. The method includes forming a plurality of isolation structures surrounding the fin structures, and a top surface of each of the isolation structures is lower than a top surface of each of the fin structures, and the isolation structures include first isolation structures over the first region and second isolation structures over the second region. The method includes forming a mask layer on the first isolation structures to expose the second isolation structures and removing a portion of the second isolation structures, such that the top surface of each of the second isolation structures is lower than the top surface of each of the first isolation structures.

In some embodiments, a method for forming a FinFET device structure is provided. The method includes forming a first fin structure and a second fin structure on a first region and a second region of a substrate, respectively and forming a mask layer over the second fin structure. The method includes etching a portion of the first fin structure to form the first fin structure with a constant fin width from a bottom portion to a top portion and forming an isolation layer over the first fin structure and the second fin structure. The method includes performing an etching process on the isolation layer to form an isolation structure on the substrate, and the isolation structure is lower than a top surface of the first fin structure and a top surface of the second fin structure, the isolation structure includes a first isolation structure over the first region and a second isolation structure over the second region. A first angle is between a sidewall surface of the first fin structure and the top surface of the first isolation structure, a second angle is between a sidewall surface of the second fin structure and the top surface of the second isolation structure, and the first angle is smaller than the second angle.

In some embodiments, a FinFET device structure is provided. The FinFET device structure includes a first isolation structure formed over a substrate and a second isolation structure formed over the substrate. The FinFET device structure includes a first fin structure extended above the first isolation structure, and the first fin structure has a constant fin width from a bottom portion to a top portion, the first fin structure has a first fin height measured from a top surface of the first fin structure to a top surface of the first isolation structure. The FinFET device structure includes a second fin structure extended above the second isolation structure, and the second fin structure has a tapered fin width which is gradually tapered from a bottom portion to a top portion, and the second fin structure has a second fin height measured from a top surface of the second fin structure to a top surface of the second isolation structure, and the first fin height is smaller than the second fin height.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming a fin field effect transistor (FinFET) device structure, comprising: forming a hard mask over a substrate; etching a portion of the substrate by using the hard mask as a mask to form a plurality of fin structures over the substrate, wherein the substrate comprises a first region and a second region; forming an isolation layer covering the fin structures and the hard mask; polishing the isolation layer to expose the hard mask; etching the isolation layer to form a plurality of isolation structures surrounding the fin structures so that a top surface of each of the isolation structures is lower than a top surface of each of the fin structures, wherein the isolation structures comprise first isolation structures over the first region and second isolation structures over the second region; forming a mask layer on the first isolation structures to expose the second isolation structures after etching the isolation layer; and removing a portion of the second isolation structures by using the mask layer as a mask, such that a top surface of each of the second isolation structures is lower than a top surface of each of the first isolation structures.
 2. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 1, further comprising: forming a gate dielectric layer over the fin structures; and forming a gate electrode layer over the gate dielectric layer.
 3. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 2, further comprising: forming a spacer layer over sidewall surfaces of the gate electrode layer; and forming an inter-layer dielectric (ILD) structure over the fin structures and next to the gate electrode layer, wherein the ILD structure has a first portion over the first region and a second portion over the second region, and a bottom surface of the first portion is higher than a bottom surface of the second portion of the ILD structure.
 4. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 1, wherein forming the plurality of fin structures over the substrate comprises: forming a first fin structure over the first region of the substrate and a second fin structure over the second region of the substrate, wherein a first angle is between a sidewall surface of the first fin structure and the top surface of each of the first isolation structure, a second angle is between a sidewall surface of the second fin structure and the top surface of each of the second isolation structures, and the first angle is smaller than the second angle.
 5. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 1, wherein forming the plurality of fin structures over the substrate comprises: forming a first fin structure over the first region of the substrate and a second fin structure over the second region of the substrate, wherein the first fin structure has a sloped sidewall surface and the second fin structure has a vertical sidewall surface.
 6. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 1, wherein forming the plurality of fin structures over the substrate comprises: forming a pad layer on the substrate; forming a hard mask layer on the pad layer; forming a photoresist layer on the hard mask layer; patterning the photoresist layer to form a patterned photoresist layer; and patterning the hard mask layer and the pad layer by using the patterned photoresist layer as a mask to form the hard mask and a patterned pad layer.
 7. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 1, wherein forming the plurality of fin structures over the substrate comprises: forming a first fin structure over the first region of the substrate and a second fin structure over the second region of the substrate, wherein the first fin structure has a vertical sidewall surface and the second fin structure has a sloped sidewall surface, and wherein after the plurality of isolation structures are formed, the vertical sidewall surface of the first fin structure is protruded from the first isolation structures and the sloped sidewall surface of the second fin structure is protruded from the second isolation structures.
 8. A method for forming a fin field effect transistor (FinFET) device structure, comprising: forming a first fin structure and a second fin structure on a first region and a second region of a substrate, respectively; forming a mask layer over the second fin structure; etching a portion of the first fin structure to form the first fin structure with a constant fin width from a bottom portion to a top portion; forming an isolation layer over the first fin structure and the second fin structure; and performing an etching process on the isolation layer to form an isolation structure on the substrate, wherein the isolation structure is lower than a top surface of the first fin structure and a top surface of the second fin structure, the isolation structure comprises a first isolation structure over the first region and a second isolation structure over the second region, and wherein a first angle is between a sidewall surface of the first fin structure and the top surface of the first isolation structure, a second angle is between a sidewall surface of the second fin structure and the top surface of the second isolation structure, and the first angle is smaller than the second angle.
 9. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 8, wherein the second fin structure has a tapered fin width which is tapered from a bottom portion to a top portion.
 10. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 8, wherein a top surface of the first isolation structure is higher than a top surface of the second isolation structure.
 11. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 8, further comprising: forming another mask layer on a first isolation structure to expose the second isolation structure; and removing a portion of the second isolation structure, such that a top surface of the first isolation structure is higher than a top surface of the second isolation structure.
 12. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 8, wherein forming the first fin structure and the second fin structure on the first region and the second region respectively comprises: forming a pad layer on the substrate; forming a hard mask layer on the pad layer; forming a photoresist layer on the hard mask layer; patterning the photoresist layer to form a patterned photoresist layer; and patterning the hard mask layer and the pad layer by using the patterned photoresist layer as a mask to form the patterned hard mask layer and the patterned pad layer; etching a portion of the substrate by using the patterned hard mask layer and the patterned pad layer as a mask.
 13. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 8, further comprising: forming a gate dielectric layer over the first fin structure and the second fin structure; and forming a gate electrode layer over the gate dielectric layer.
 14. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 13, further comprising: forming a spacer layer over sidewall surfaces of the gate electrode layer; and forming an inter-layer dielectric (ILD) structure over the first fin structure, the second fin structure and next to the gate electrode layer, wherein the ILD structure has a first portion over the first region and a second portion over the second region, and a bottom surface of the first portion is higher than a bottom surface of the second portion of the ILD structure.
 15. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 14, further comprising: forming another first fin structure above the first isolation structure, wherein a first pitch is between the first fin structure and another first fin structure; forming another second fin structure above the second isolation structure, wherein a second pitch is between the second fin structure and another second fin structure, and the second pitch is greater than the first pitch.
 16. A method for forming a fin field effect transistor (FinFET) device structure, comprising: forming a first fin structure and a second fin structure on a first region and a second region of a substrate, respectively, wherein the first fin structure has a vertical sidewall surface, and the second fin structure has a sloped sidewall surface; forming an isolation layer over the first fin structure and the second fin structure; performing a polishing process on the isolation layer; performing an etching process on the isolation layer, wherein a top surface of the isolation layer is lower than a top surface of the first fin structure; forming a mask layer over the first fin structure after performing the etching process on the isolation layer; etching a portion of the isolation layer adjacent to the second fin structure to form an isolation structure on the substrate, wherein the isolation structure comprises a first isolation structure in the first region and a second isolation structure in the second region, and a top surface of the first isolation structure is higher than a top surface of the second isolation structure.
 17. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 16, further comprising: forming a dielectric layer over the first fin structure; and forming a second mask layer over the dielectric layer, wherein a top surface of the second mask layer is exposed when performing the polishing process on the isolation layer.
 18. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 17, further comprising: removing the dielectric layer and the second mask layer when performing the etching process on the isolation layer.
 19. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 16, further comprising: forming an inter-layer dielectric (ILD) structure over the first fin structure, the second fin structure, wherein the ILD structure has a first portion over the first region and a second portion over the second region, and a bottom surface of the first portion is higher than a bottom surface of the second portion of the ILD structure.
 20. The method for forming the fin field effect transistor (FinFET) device structure as claimed in claim 16, wherein the first fin structure has a first bottom portion embedded in the first isolation structure, the second fin structure has a second bottom portion embedded in the second isolation structure, and the a first height of the first bottom portion is greater than a second height of the second bottom portion. 